The present invention relates to the art of color proofing. In particular, to an improved endless belt used in a lamination assembly for preparing prepress color proofs, such as by the use of pressure and heat to laminate media together.
Prepress color proofing is a procedure used in the printing industry, to create representative images of printed material. The representative images are used to check for color balance and other important image quality control parameters, without the high cost and time that is required to actually produce printing plates and set up a printing press to produce an example of a representative image. These representative images may require several corrections and may be reproduced several times to satisfy or meet the requirements of the customer, resulting in a large loss of profits and ultimately high costs to the customer.
Generally speaking pre-press color proofs sometimes-called xe2x80x9coff pressxe2x80x9d proofs or prepress proofs, are one of three types. One a color overlay that employs an image on a separate base for each color. Two a single integral sheet process in which the separate color images are transferred by lamination onto a single base. And third a digital method in which the images are produced directly onto or transferred by lamination onto a single base from digital data.
In one typical process for a prepress color proofing system used in the printing industry, a multicolor original is separated into individual transparencies, called color separations, the three subtractive primaries and black. Typically a color scanner is used to create the color separations and in some instances more than four-color separations are used. The color separations are then used to create a color proof sometimes-called an xe2x80x9coff pressxe2x80x9d proof or prepress proof as described above.
A color proofing laminator can be used to bond lamination sheets to receiver stock as a part of a color proofing system. The lamination sheets include a carrier and a layer of material to be applied to the receiver stock, which, in the case of a typical laminator, is a color donor. A lamination sheet is laid upon the receiver stock with the color donor end sandwiched between the carrier and the receiver stock forming a lamination sandwich.
A related laminator is described in U.S. Pat. No. 5,478,434. As shown in that FIG. 1, a lamination sandwich 10 sits on an entrance table 20. A leading edge of lamination sandwich 10 is fed into a laminator 12 which includes an upper pressure roller and a lower pressure roller. Lamination sandwich 10 thereafter exits the upper and lower pressure rollers can be heated rollers. Upper pressure roller and the lower pressure roller come to rest on an exit table 14 undisturbed until the trailing edge is cool to the touch; whereupon the top-most carrier can be peeled away from receiver stock and from the transferred color donor. With the configuration of an upper pressure roller and a lower pressure roller as described above, the laminator is called a straight-through laminator. Further details of this type of lamination/delamination system can be found in the above. As an additional reference, U.S. Pat. No. 5,203,942 describes a lamination/delamination system as applied to a drum laminator.
While the above-described laminator works well for a few materials and in limited conditions, there are many conditions and materials that cannot be laminated successfully using the above-described laminator. Accordingly, belt laminators have been invented. A belt laminator using an endless belt is generally made by one of two manufacturing methods, dip skived or spun cast. Both methods have a relatively high cost and thickness of the belt is limited to an approximate range of 50 to 150 microns.
Both belt manufacturing process tend to have built in stresses which when used in a lamination application, form ripples that are transferred to the intended image making the intended image unacceptable. It should be noted that ripple, may also be caused by the lamination rollers used in the laminator. With the dip skived method of manufacturing for an endless belt, problems develop because it is difficult to manufacture without pinholes through the material caused by air bubbles which occur in the material to make the belt when that material is in the liquid state or during solvent out gassing during the curing process. This manufacturing defect can be easily transferred to the intended image, making the intended image unacceptable.
The present invention provides for an endless belt for a laminator, which overcomes the drawbacks noted above. The present invention provides an endless belt that allows for a larger thickness range to overcome ripple.
The present invention also provides an endless belt for a laminator that can be orientated to overcome the stresses that are built in the manufacturing process.
The present invention further provides an endless belt for a laminator that overcomes the pinholes that are formed in the manufacturing process.